Using custom objects that came from extension

The story is that I have external .NET dll that was provided by the producer of the web service. In order to use it I created extension to add there the dll provided. The methods of the wrappers return complex typed objects (classes that are defined in this dll). I would like to get this result objects in my eSpace module but I don't see how can I use them because there is only Object type that I can return from extension methods. I can't return custom object types. Even though, let's assume I got these custom objects in eSpace module, how can I work with them (get properties)? Maybe it is possible to create structures to be able to transfer custome object properties into structure? How do you deal with custom data types returned from extensions?